The present technology relates to a receiver, reception method, program and reception system that can provide improved reception performance for receiving a signal with a variable bandwidth.
In terrestrial digital broadcasting, for example, channels (physical channels) are generally defined to be spaced at constant frequency intervals so as to transmit independent signals with bandwidths prescribed by laws and regulations. A guard band with a given bandwidth is established between each pair of adjacent channels in order to prevent, for example, interchannel interference.
In the case of DVB-T/T2 (Digital Video Broadcasting-Terrestrial/Terrestrial 2), i.e., the European terrestrial digital broadcasting standard, for example, the channels are each 8 MHz in bandwidth as illustrated in FIG. 1A. Receivers are designed based on the premise that signals with a predetermined bandwidth will be transmitted.
In the event of presence of an interference wave in some channels (physical channels) of a band, transmission operators that transmitted signals using such a transmission system have chosen not to use the entire band, thus resulting in wasteful use of a frequency band.
Incidentally, DVB-C2 (Digital Video Broadcasting-Cable 2) that was standardized in 2010 as the European second generation cable digital broadcasting standard includes an arrangement adapted to avoid such a waste (refer to DVB-C2 Standard Document [Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital transmission system for cable systems (DVB-C2)] DVB Document A138, hereinafter referred to as Non-Patent Document 1).
As illustrated in FIG. 1B, DVB-C2 supports the concept of data slices, and a predetermined number of such data slices are combined together to make up a C2 system. The data slices are each 3408 carriers or less in bandwidth and may be freely combined as long as the conditions specified by the standard are met.
DVB-C2 also supports the concept of notches. Transmission operators can define the band unavailable due, for example, to external interference as a notch and include subcarrier-by-subcarrier notch position information in the C2 system.
FIG. 2A is a diagram illustrating an example of a DVB-T/T2 signal, and FIG. 2B is a diagram illustrating an example of a DVB-C2 signal. In FIGS. 2A and 2B, the horizontal axis represents the frequency. A description will be given below of a DVB-C2 signal.
As enclosed by a line in FIG. 2B, a C2 system includes a preamble symbol and data symbol. As far as the standard is concerned, one C2 system is a signal having a bandwidth of up to about 3.5 GHz.
A preamble symbol is used to transmit transmission control information called L1 signalling part 2 data (L1 information). The L1 information will be described in detail later. The same information is repeatedly transmitted at intervals of 3408 carriers (3408 OFDM (Orthogonal Frequency Division Multiplex) subcarriers) using a preamble symbol. The 3408 carriers correspond to a 7.61 MHz frequency band.
A data symbol is used to transmit transport streams (TS) such as program data. A data symbol is divided for each data slice. For example, data slice 1 (DS1) and data slice 2 (DS2) carry different pieces of program data. The parameters relating to each data slice such as the data slice count are contained in L1 information.
The portions filled with black in FIG. 2B are notches. Notches are frequency bands used, for example, for FM broadcasting, police wireless communications and military wireless communications, and are not used to transmit C2 system signals. In a transmission signal output from the transmitter, the notch periods are signal-free periods. Notches can be classified into two types, narrowband notches of less than 48 carriers in bandwidth and broadband notches of 48 carriers or more in bandwidth. The parameters relating to each notch such as the notch count and bandwidth are contained in L1 information.
As described above, a DVB-C2 signal has “data slices” and “notches” that are variable in bandwidth. It is necessary for the receiver to demodulate an OFDM signal whose bandwidth is selected almost at will by the transmitting side. In DVB-C2, the desired width of a data slice may be smaller than 3408 carriers. The desired data slice count is acquired from L1 information during channel scan.
The reception process by the receiver is conducted by receiving a signal within a tuning window with a fixed bandwidth (3409 carriers) as illustrated in FIG. 3A. The center position (center frequency) of the tuning window suitable for receiving a desired data slice signal is specified by the transmitting side.
The receiver demodulates the OFDM signal by orthogonally demodulating the signal using a signal whose frequency has been specified by the transmitting side. The program data is decoded based on the L1 information obtained from the demodulation.